1. Field of the Invention
The invention relates to an electric power steering (EPS) apparatus and a controlling method for the same.
2. Description of Related Art
As described in, for example, Japanese Patent Application Publication No. 2010-155598 (JP 2010-155598 A), an EPS apparatus applies the torque of a motor to the steering mechanism of a vehicle to assist the steering operation of a driver. The EPS performs the feedback control of motor current to generate an appropriate assist force according to at least a steering torque. That is, the EPS adjusts motor application voltage through the adjustment of a PWM duty to reduce the difference between an assist current command value calculated based on at least a steering torque and a motor current detection value.
In order to respond to requests for high safety, the EPS of JP 2010-155598 A employs the following configuration. That is, the EPS limits an assist current command value to a preset upper or lower limit when the directions of a steering torque and an assist current command value agree with each other. On the other hand, when the directions of a steering torque and an assist current command value are opposite to each other, the EPS determines that abnormality has occurred in assist control calculation and limits the assist current command value to zero.